For example: It's a rock of crack cocaine found in a man's pocket. It's a department-store security video showing a woman slipping a necklace into her handbag. It's a blood test showing a driver's blood-alcohol level above the legal limit.

Bob Dekle, who prosecuted serial killer Ted Bundy and is now a professor at the Levin College of Law at the University of Florida, characterized probable cause as "just above suspicion."

In the case of Trayvon's shooting death,it would be any piece of evidence that would convince a judge that Zimmerman probably committed a crime when he shot the unarmed teen in a gated Sanford community in late February.

That could be a witness, a piece of physical evidence or something else.

Sanford police were looking for evidence of manslaughter. Special Prosecutor Angela Corey will not say what charge or charges her team is reviewing.

Police can and do arrest suspects without probable cause, but judges must then order their release from jail. Senior Judge O.H. Eaton Jr. said that happened at least once or twice every weekend he was on jail duty reviewing Seminole County arrests for the previous 24 hours.

When that happens, police can rearrest the suspect, and prosecutors are free to file charges. But they must bring the case to trial within 175 days ofarrest, according to Florida rules of criminal procedure.

That ticking clock is often an incentive for prosecutors to hold off on an arrest, they said. It gives them more time to collect evidence — for example, to get ballistics tests done if a gun is involved or to have fingerprints analyzed.

Prosecutors almost always demand more evidence than cops.

Though an officer needs only probable cause to make an arrest, prosecutors typically want enough evidence for a conviction — enough to convince a jury beyond every reasonable doubt that the suspect is guilty.

It is a natural point of friction between the two branches of law enforcement, said Ric Ridgway, chief assistant state attorney in the 5th Judicial Circuit, which includes Lake County.

"It's probably the single most frequent source of … disagreement between law enforcement and prosecutors, between victim's families and prosecutors," he said. "They look at it and go, 'We know he did it.' As a prosecutor, I say, 'Can you prove it?' "

Evidence standards

Because of those different evidence standards, prosecutors typically kick loose at least a quarter of the cases in which police make arrests, he said.

That happened in the case of four co-defendants in the Jessica Lunsford murder, Ridgway said. The 9-year-old Homosassa girl was abducted, raped and buried alive in 2005. Prosecutors convicted suspect John Couey, the kidnapper and killer, but Citrus County deputies and prosecutors disagreed about what to do with four of his roommates.

Deputies arrested them on charges of obstructing an officer — withholding information.

"We would not prosecute them," Ridgway said, because there wasn't enough evidence for a conviction.

Sometimes police and prosecutors work a long time to gather enough evidence before making an arrest.

A Seminole County grand jury in February handed up a murder indictment in a 21-year-old homicide: Betty Claire Foster was stabbed to death at the Casselberry computer store where she worked in 1991. David Lee Hedrick, 50, a computer and audiovisual specialist, is now in the Seminole County Jail, awaiting trial.

A Brevard County grand jury last year indicted a woman there on a first-degree-murder charge in a three-year-old homicide.

And in Orange County, Brett Ballard and his wife, Joy, have been waiting more than three years to find out whether the security guard who fatally stabbed their 20-year-old son, Marcus, in 2008 will be arrested and prosecuted.

Marcus Ballard was stabbed eight times in the torso and neck and several times on the palms of his hands, according to his autopsy. The security guard told deputies the men were fighting at a Pine Hills apartment complex and he used his knife to defend himselfafter Ballard had begun choking him.

Sometimes, mistakes

Police and prosecutors sometimes get it wrong.

An officer was dispatched to a Miami-Dade County neighborhood in response to a reported burglary. About that same time, a black 15-year-old, his brother and a friend ducked into a neighbor's carport because of a sudden rain, according to an appeals-court ruling.

The officer saw the boys, drew his weapon, and the 15-year-old took off running and hid. An officer soon found him, ordered him facedown in the mud, handcuffed him and arrested him on a charge of resisting an officer without violence, according to the ruling.

The Third District Court of Appeal in May 2010 reversed the juvenile court's finding in the case, ruling that the police officer should never have made the arrest.